Cheryl Corley

When the bell rings at Chicago's Sullivan High School on the city's far north side, it's a familiar scene. Hundreds of students pour into the hallway heading to their next class. What's also becoming increasingly familiar is the presence of two uniformed police officers in the hallway keeping watch. The school resource officers often chat with the students passing by and Sullivan's principal Chad Adams says the officers provide a higher level of security for the school and much more.

A fatal police shooting in Kansas late last month focused attention again on how so-called swatting — prank 911 calls designed to get SWAT teams to deploy — puts lives at risk and burdens police departments.

There are more than 7,000 911 centers in the U.S. and, according to the National Emergency Number Association, they receive about 600,000 calls a day. Authorities don't track swatting calls nationally, though the FBI has been monitoring the practice of those types of fake calls for about a decade.

If you've ever called 911 to report an emergency, thank the Johnson Crime Commission. Establishing a national emergency number was just one of more than 200 recommendations the Commission offered up in a landmark 1967 report "for a safer and more just society."